This invention relates generally to cryogenic glass-to-metal type vacuum seals and more particularly to a novel seal structure and method for producing a seal which maintains a vacuum with minimal stress at low temperature.
Existing cryogenic vacuum systems having optical ports generally comprise windows of substantially flat glass plates bolted onto a flange with metal or rubber gaskets. The glass-to-metal type seal structures of existing systems generally include gaskets of Kovar.sup..TM., stainless steel, and copper or like structures which tend to lose their seal and require remount after a thermal cycle to cryogenic temperatures.
The present invention provides a low temperature vacuum seal structure between a nonmetallic element, such as an optical port, and a metallic element or housing wherein thin metallic layers are applied to the nonmetallic element for adhesion and solderability and a metallic layer is applied to the housing for solderability, and a solder layer (e.g., indium) interfaces the layers on the nonmetallic element and housing to provide a vacuum seal therebetween.
The seal structure and method of the present invention may find substantial utility within closed cryogenic vacuum systems having optical ports exposed to the cryogenic temperatures, such as in laser systems utilizing vacuum enclosures. Nonmetallics sealable according to the invention may comprise a wide variety of materials including glass, fused silica, quartz, or semiconductor material such as ZnSe for use with the infrared output of a laser. Optics mounted with the seal structure according to the present invention may function at cryogenic temperatures without frequent remounting or resealing. Optical elements comprising lenses, aspherics and the like, including coated optics and dielectrics, may be bonded and sealed directly to substantially any type of receiving metallic housing without the use of adhesives, gaskets or washers, and the optical elements may assume substantially any size or shape, and yet retain a seal against radiation exposure and repeated thermal cycling between about -330.degree. F. and about +250.degree. F.
It is therefore, a principal object of the present invention to provide an improved nonmetal-to-metal seal.
It is a further object of the invention to provide an improved seal structure which will maintain a vacuum at low temperature.
It is a further object of the invention to provide an improved seal structure which will maintain low stress in the nonmetallic element at low temperatures.
It is yet another object of the invention to provide an improved low temperature vacuum sealed laser window.
It is a further object of the invention to provide an improved method for making a cryogenic glass-to-metal type vacuum seal.
These and other other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.